[HELP] cross-compile gtk application to ARM raspberry

[MassiminoilTrace]

Hello, let me know if this is the right repository to ask.

I'm trying to cross-compile a simple rust GTK application on an Ubuntu 20.04 LTS from amd64 to ARM architecture for a raspberry2 (arm v6).

I first tried to cross-compile following some tutorials, but I encountered an issue about pkg-config which I'm not able to solve and I can't find any resources about :/ I've already set the gcc arm linker for that target in ~/.cargo/config.

When I run cargo build --target arm-unknown-linux-gnueabihf i get:

The following warnings were emitted during compilation:

warning: pkg-config has not been configured to support cross-compilation.

error: failed to run custom build command for `gio-sys v0.16.0 (https://github.com/gtk-rs/gtk-rs-core.git#e6104a2d)`

Caused by:
  process didn't exit successfully: `/home/massimo/Documenti/Programmi/gtk-test/target/debug/build/gio-sys-5f3d520153a7586a/build-script-build` (exit status: 1)
  --- stdout
  cargo:rerun-if-env-changed=GIO_2.0_NO_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_arm-unknown-linux-gnueabihf
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_arm_unknown_linux_gnueabihf
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG_arm-unknown-linux-gnueabihf
  cargo:rerun-if-env-changed=PKG_CONFIG_arm_unknown_linux_gnueabihf
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_arm-unknown-linux-gnueabihf
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_arm_unknown_linux_gnueabihf
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_SYSROOT_DIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR
  cargo:warning=pkg-config has not been configured to support cross-compilation.

  Install a sysroot for the target platform and configure it via
  PKG_CONFIG_SYSROOT_DIR and PKG_CONFIG_PATH, or install a
  cross-compiling wrapper for pkg-config and set it via
  PKG_CONFIG environment variable.
warning: build failed, waiting for other jobs to finish...
error: build failed

I hope to contribute in writing some step by step guide if i manage to solve this cross-compile stuff, so maybe it can be added to the docs for everyone to use.

Thank you anyway

[sdroege]

The error tells you what do do :) You need to configure pkg-config correctly for your ARM sysroot.

[MassiminoilTrace]

Thanks, I guess the issue was on my side, not knowing enough about what sysroots are and not finding enough information :/

After few more hours of research I managed to complete the compilation, I'll test the binary hoping it works.

If it works, what's the best place I could contribute to by adding some tutorial?

[GuillaumeGomez]

I think the best place would be the gtk4 book. Also: it would be very appreciated. :)

[MassiminoilTrace]

Seems the problem wasn't so easy as it seemed >.<

I made a folder with all the libraries from my raspberry 2 to use as a sysroot, then set in ~.cargo/config

[target.arm-unknown-linux-gnueabihf]
linker = "arm-linux-gnueabihf-gcc"
rustflags = ["-C", "link-args=--sysroot=/home/massimo/sysroot_pi"]

I also added an environment variable for pkgconfig

export PKG_CONFIG_SYSROOT_DIR="/home/massimo/sysroot_pi"

Everything seems to compile, but it generates a Segmentation fault when run on my raspberry pi 2.

It seems that gcc doesn't link and create correct binaries for armv6 https://stackoverflow.com/a/65186762. Running arm-linux-gnueabihf-readelf -A ./gtk-test gives me a Tag_CPU_arch: v7, so I'm kind of stuck. This project recompiles the whole gcc from scratch in a container to solve it, maybe there's an easier solution?

In any case, I'll test if the overall process at least works for newer raspberry with target.armv7-unknown-linux-gnueabihf triplet

[sdroege]

You'll have to get and configure a toolchain for the correct target platform, yes.

[bilelmoussaoui]

Let us close this, if you think such information could be useful as part of the gtk4-rs book then please either open a detailed issue there or send a PR :)